When manufacturing turbo aero engines for aircraft, it has been deemed essential to carry out a prestressed shot-blasting on the internal surfaces of the rotor. This surface treatment is able to reinforce the mechanical and protective capacities of the surfaces in question.
Shot-blasting consists of projecting at high speed metal balls having a diameter of between about 0.2 and 0.6 mm. This hammering makes it possible to obtain the expected treatment of the surfaces.
The rotor of a turbo aero engine internally possesses a large number of radial grooves known as stiffeners which form a large number of internal annular cavities which also need to be shot-blasted. The difficulty of carrying out this operation has compelled turbo aero engine manufacturers to produce these rotors made up of several sections so as to be able to gain access to the internal surfaces to be treated by means of shot-blasting. Accordingly, the structure of the rotor lacks homogeneity.
The main object of the invention is to be able to produce a turbo aero engine rotor formed of a single piece whilst allowing for the shot-blasting of all the internal surfaces needing to be treated by this method.
The shot-blasting technique consists of projecting at high speed metallic balls with the aid of one or several high pressure compressed air sources. The balls are thus carried in pipes ending at a terminal projection nozzle. It can be readily understood that the least change of direction on the passage of the flows of balls propelled at high pressure inside the pipe constitutes a significant loss of head and power. The efficiency of the shot-blasting installation is thus dependent on pitfalls of this type. Now, the internal cavities of a turbo aero engine rotor are inaccessible by a straight pipe. In fact, they are indeed not visible. They are only accessible by the central pipe of the rotor where each of these cavities opens onto. In other words, the internal cavities of a turbo aero engine rotor are virtually inaccessible to shot-blasting having sufficient power.
Secondly, an excess pressure shot-blasting installation includes:
a shot tank or shot feed means; PA1 means for propelling this shot under pressure, such as compressed air means; PA1 one or several shot-blasting pipes for bringing the shot under pressure to a projection nozzle, and PA1 the projection nozzle in question being placed at the end of the pipe. PA1 a shot feeding pipe; PA1 high pressure compressed air means for propelling the shot and connected to the outlet of the feeding pipe; PA1 at least one shot-blasting pipe so as to bring the shot under pressure close to the surfaces to be shot-blasted and connected to the propulsion device, and PA1 a projection nozzle placed at the end of the shot-blasting pipe. PA1 the shot-blasting pipe is rectilinear; PA1 the propulsion means include two high pressure compressed air pipes opening on both sides of a right-angle bend or elbow which receives at its inlet the feeding pipe, the sudden change of direction of the shot flow being ensured by this right-angle bend prior to connection with the compressed air pipes so that the propulsion energy is only sent to the shot at the inlet of the rectilinear shot-blasting pipe opening onto the projection nozzle. PA1 a vane type turbine having its spin axis merged with the axis of the shot-blasting pipe, and PA1 a third compressed air pipe opening tangentially with respect to the vertical spin axis opposite the vanes of the turbine so as to have the shot-blasting pipe and projection nozzle rotate in a rotation direction opposing that of the bayonet device. The device may advantageously be completed by an adjusting screw so as to slow down or block rotation of the turbine.
The shot-blasting pipe(s) thus need to comprise sudden changes of direction. The same applies for the projection nozzle which may be brought to be provided with a deviation surface known as a projection anvil according to the position and orientation of the surfaces to be treated.